Euro Retreats From $1.37

NEW YORK—The euro saw its biggest one-day drop in more than a month as political uncertainty in Spain and Italy revived fears about the region's financial stability.

Markets in Europe were shaken by allegations of secret cash payments to Spanish Prime Minister Mariano Rajoy, while in Italy, former Prime Minister Silvio Berlusconi, who has promised to reverse the conservative fiscal policies of his predecessor if he is reelected, has...